Hitherto, in broadcasting studios, a live image photographed with a live camera and a computer graphic image produced by a computer have been synthesized together by employing a chromakey technique, and the resultant synthesized image has been broadcasted.
For example, when producing with a chromakey technique an image such that a person is present in virtual space produced by computer graphics, a person is caused to stand in front of background with a predetermined hue (e.g., colors which are not contained in the image of a person, such as blue and green), and the person is photographed. Then, a key signal is produced from the video signal with the hue of the background as a reference, and based on the key signal, the background is replaced with an image produced by computer graphics. This makes it possible to synthesize a computer graphic image and a person together and produce such an image as if the person is present in virtual space produced by computer graphics.
Incidentally, in such a conventional image synthesizer employing a chromakey technique, when the camera is moved, there is the disadvantage that the synthesized background (i.e., an image produced by computer graphics in the aforementioned example) does not change in correspondence with the movement of the camera. If image synthesis can be performed so that the image of a synthesized background is also changed naturally in correspondence with such movement of the camera, it is believed that an image synthesized by this kind of image synthesis can be made even more realistic.